This invention relates to a detecting system for sensing a rotatable shaft to determine its speed and torque.
Systems have been developed having transducers for producing a magnetic field adjacent to a rotating shaft and for measuring the changes in that magnetic field to provide information regarding different shaft characteristics, such as speed, torque and horsepower. It has been known that as a driven or loaded shaft is torsionally stressed, compression and tension occur in various portions of the shaft and this changes the shaft permeability and consequently the magnetic flux pattern in the shaft thereby to alter the magnetic field. A torque information signal may be developed from the altered magnetic field. Such a system is disclosed in U.S. Pat. No. 4,100,794, issued July 18, 1978 in the name of Edwin J. Meixner, and which is assigned to the assignee of the present invention. In addition, it is recognized in U.S. Pat. No. 4,100,794 that the magnetic field also varies as a function of the shaft speed due to the armature reaction in the shaft. Eddy currents will flow on the surface of the rotating shaft and produce a counter magnetic field which opposes and distorts the original magnetic field. The faster the rotational speed, the greater the eddy current flow and the greater the amount of field distortion. As a result, the resultant magnetic field may be used to generate a speed-indicating signal.
While the amplitudes of the torque and speed signals vary linearly with respect to the actual torque and speed, respectively, as those parameters approach zero in the system of U.S. Pat. No. 4,100,794, with the present invention the linearity of both of those torque and speed signals may be extended all the way to and through zero torque and zero RPM respectively. This, of course, improves the performance.